“ With a huge number of sacrificial victims, another realm long ago secretly bound a Prince of the land spirits, Iorstonn by name, thus ensuring the fertility, and improving the magical defences, of their realm. But binding that Prince to one spot has disrupted the weather and magical patterns (ley lines?) over half the continent. Things have become bad enough that a coalition has been formed to rectify the situation, once divinations have established the cause.
Your party is one of the teams assembled to do the rectification: find the binding object and steal it ('so that we can destroy it here in our realm, of course'...*) or destroy it over there. Presumably the Prince will be grateful to his rescuers and angry at the binders, but with a greater spirit like Iorstonn one can never be sure: such beings are 'tricksy'.
* Of course, the rulers of our realm might want to control Iorstonn for their own ends...”
“ This really comes from an ancient Chinese novel. Imagine during the PCs' travels, they come to a place where the gender roles are completely reversed. What adventures will the PCs encounter in such a place?”
“ You've probebly heard of the real Thomas Hopkins, Witchfinder-General, who hunted down and hanged suspected 'witches'. What if there was a world/realm where magic was normal, and it was the non-witches and non-wizards who were hunted down and hanged as inferior beings?”